The merozoite interacts in a receptor specific manner with the erythrocyte surface and is the stage upon which immunity may work to block invasion. Thus, merozoite surface components are of interest because of their role in erythrocyte recognition and as antigens for induction of protective immunity. We are identifying P. knowlesi, P. vivax and P. falciparum receptors for attachment to monkey and human erythrocytes. To understand the molecular basis for this variation we are studying one antigen on the merozoite surface that undergoes antigenic variation. The components in the junction and the signaling after merozoites make contact with erythrocytes is also under study.